Question

I have an object which I initialize in the app’s main thread but I call one of its methods in a background thread using performSelectorInBakground. However, the method seems to be unresponsive. More specifically :

AccHandler.m

#import "AccHandler.h"

@implementation AccHandler
@synthesize accelerationOnYaxis;
-(void)startAccelerationUpdates
{
    CMMotionManager *motionManager = [[CMMotionManager alloc] init];
    motionManager.deviceMotionUpdateInterval = 0.01; 
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
     {
         self.accelerationOnYaxis = motion.userAcceleration.y;
     }
     ];
}
@end

Tester.m

#import "Tester.h"

@interface Tester()
{
   AccHandler *accHandler;
}
@end

@implementation Tester
- (id) init
{
    //....
    accHandler = [[AccHandler alloc] init]; // initialized in main thread
}

-(void)test
{
    [accHandler startAccelerationUpdates]; // but -(void)test will be executed in a background thread..
    NSLog(@"current acceleration is %f", accHandler.accelerationOnYaxis;
}

later on in my code I call the test method from a performSelectorInBackground but I get 0 acceleration values..

Answer 1

Can one object be initialized in the main thread and have its methods
executed in a separate thread?

Yes.

Your mistake seems to be that you are not waiting for the background stuff to produce results.

Another problem might be that motionManager does not seem to be retained by some strong reference. So it might just immediately go away after initialization.